1979 Johnson 235 Power loss under load, forward gear only.

[Hooligan Diver]

New member, seeking advise.
I had the boat out on the Gulf scalloping yesterday and wasn't able to make power in forward gear. It will rev OK in neutral, and has normal power in reverse, but wont get above 1800rpm in forward gear under a load. It did, spring to life once, and ran fine until I backed out of it, never achieved plane speed again.
Any suggestions were I should begin to trouble shoot?
Thanks, Chuck.

 

[Hooligan Diver]

I will add, that there were a few instances, when it wouldn't rev well in neutral either. Strangely enough, it still revved fine in reverse....

 

[emdsapmgr]

Possible that it's not firing on all 6 cyls. That engine will seem to run fine on 3 or 4 cyls in neutral or when on the trailer. Check for spark after the engine is well warmed up. Weak ignition components typically work when cold, then fail once the engine heats up to normal operating temps. You can check by doing a cyl drop test or use an inductive timing light to show spark on each plugwire.

 

[Hooligan Diver]

I can understand how that's possible, just seems odd, it was running so well last season...
I'll locate a timing light as soon as possible. In the mean time, is there a test I can do, other than using a screwdriver to arc the plugs to the block?

 

[Will Bark]

Warm the engine up on trailer, in a tub or on the muffs; then pull each plug wire with the engine running one at a time if no change then that plug is not firing; if change then it's firing. Do this for all plugs and see whose firing and whose not. Good luck

 

[Hooligan Diver]

Well, after running on muffs, pulling plug wires 1 at a time, It seems the top 2 cylinders on the port side are not firing.....cdi?

 

[Hooligan Diver]

I also noted that the center coil on the starboard side was arcing to the engine block when the plug was pulled, no others did so.

 

[Hooligan Diver]

After cross referencing part numbers, I believe the pack from my '87 70hp is compatible.....I'll confirm tomorrow morning, but I might get lucky and be able to change them out to see if this is the problem.

 

[Hooligan Diver]

Well, I decided against installing the pack from the other engine. I'll be needing it in order as well next week anyway, and after close inspection I was unhappy with the way many of the coils and plug wires looked. Some were older than others, and the power packs were definitely many years apart in age.
I went for broke and ordered a pair of packs and all new coils and wires, they'll be here tomorrow afternoon. I feel it was well spent money, just really hopefull it takes care of things. We are leaving Saturday for a week on the gulf.

 

[Hooligan Diver]

Packs and coils came in a day late.
Some of the components have previously been replaced with newer parts and have had plug connections modified. Looks like I'm going to have to do the same in order to install all the new ones......cross referencing shows I have suitable packs, (sierra763796) but it's going to be a modification to get'em installed.

 

[Hooligan Diver]

Well, I got all new power packs coils and plug wires installed. Firing on all 6 now, but running rougher than before, and will not idle.
Is there anything I should know about timing/retiming after changing all these out, how would I go about it if so?

 

[Hooligan Diver]

Running out of time to smoothe this thing out... hate to trailer it 50 miles this way, but can't help thinking it's something really simple/minor that I'm not aware of at the moment.

 

[racerone]

Compression test results are ??

 

[emdsapmgr]

Are you sure that you have the packs matched correctly to each coil? The pack wires to each coil should be color coded. If they are hooked up wrong, the engine may run but may backfire and run with no power.

 

[Hooligan Diver]

No compression test done, not a concern at the time. I've owned it for a couple years and don't suspect anything internal is wrong.
I did have to connect all of the new coils individually instead of using a plug connector as roughly half of them had been replaced already with newer parts than the rest.
It does seem like it could be something like that.It ran pretty well before I replaced the packs and coils other than a slight skip every now and then, but is much rougher now, and tends to "pop" or backfire slightly as I have to maintain about 2000rpm to keep it running. It will not idle, but rather stops abruptly when throttle is backed to idle position.
I'm pretty obsessive when it comes to stuff like this wiring, but there's a chance I could have mixed a wire up somewhere I suppose. I'll have to go over it in a couple of hours.
I really appreciate the replies, I'm in a pinch with 11 people counting on a working boat for a week of scalloping that is due to start this afternoon..........

 

[Hooligan Diver]

On the power pack, there are 3 orange coil feed wires. The configuration, based on the power packs is as follows; orange with green tracer #1&2, orange with no tracer 3&4, and orange with purple tracer #5&6.

 

[racerone]

Grass is green so the orange and green go on 5 / 6---The sky is blue so blue / purple go to 1 / 2 on these motors.

 

[Hooligan Diver]

You're the man racerone!
You just helped me save a family vacation, THANK YOU.
I did in fact have the top and bottom cylinders crossed. Switched out long plug wires to reroute fire for a test and it's running better than it has since I've owned it. I'll be running it this week with the temporary spark plug wire arrangement and reconfiguring the coil locations when we return as to avoid future confusion.
A big thanks to those whom contributed to this thread. These forums are certainly a must for boat owners in my opinion.

 

[racerone]

Do the compression test and check high speed jets on the top carburetor.